This ain't no fucking sing-alongSo, girl, what you singing for?

He’s referring to girls singing around him thinking they will get their big break if he hears their voice. Hence the “because we’re blowing like a C4.” The girls are trying to ride them — no pun intended — to the top..

This might be about the Mod Club show that ended up a live release. Over all the songs you just hear girls singing and telling him they love him. He’s saying that it’s a concert, not some chance to profess your love and get your voice on the live recording. Just listen to The Weeknd Live @ Mod Club.